Problem: What do the following two equations represent? $x+y = 3$ $-5x-5y = -15$
Solution: Putting the first equation in $y = mx + b$ form gives: $x+y = 3$ $y = -x+3$ Putting the second equation in $y = mx + b$ form gives: $-5x-5y = -15$ $-5y = 5x-15$ $y = -1x + 3$ The above equations turn into the same equation, so they represent equal lines.